Reverse hammer for the spotter with his own hands

Materials required

The iron for the spotter is allocated in the volume of 35-40 sq. see. On thyristor overheating is not observed. They are marked on the spots, which are after the cable. Overheating is subject to the rod on the basis of black metal. Its diameter is 16 mm. It should preferably be made of brass.

If we talk about the cable for the spotter, it is taken with a cross section of 70 kV. mm, and a length of 1.7 m and 2.1 m is sufficient for the weight and the hammer. Provide pulse control of the thyristor (TH-40).

The secondary winding of the transformer is wound by means of a 6.5 x 4 copper bar in the third winding. It is also possible to replace it with an aluminum. Two more coils are added to the secondary winding. Finally, the apparatus should contain an aluminum transformer winding of 250 kV. mm, which corresponds to five windings with six coils.

How it works?

The principle of operation is based on the release of heat at the point of contact of two connected parts when electricity is flowing. It is the principle of contact welding. To the place of connection the device delivers an electric current of 3000 to 5000 A per 1 millimeter of thickness of the metal part. Due to this, in the place of contact, the metal is heated almost to the point of melting. The elements are pressed together very firmly using mechanical force or by using pneumatic pliers for one second.

There are two techniques for straightening dents on car bodies. The first involves squeezing from the inside. But to do this, you need to remove the element. The second technology is extrusion from the outside using a spotter for body repair. This is a more common variant.

An inverter-based device

Homemade spot welding machines, made on the basis of a welding inverter, have a simple design, have the necessary power to work with most metals and can easily be made with their own hands.

The simplest spotters can consist of the following elements:

The easiest way to make such a machine for contact welding using inverters, to which a welding gun is attached through a cable. It is possible to use ready to buy stadding guns as well as to make them on the basis of metal sealant gun.

Advantages of self-made spotters:

  • Ability to pull metal parts without damaging the original paint layer.
  • Convenience in operation.
  • Versatility of use.
  • Possibility to perform metal deposition using graphite electrodes.
  • Availability of two or more welding modes.
  • Ease of construction.
  • Affordable cost of components used.

It is possible to find various schemes of manufacturing of inverter spotters. You can choose both the simplest models that are designed for domestic use and professional units combining power, versatility of use and advanced capabilities.

You will need the following components to assemble the machine yourself:

  • 220 volt contact group.
  • Diode bridge.
  • Control relay for 30A.
  • Transformer that reduces the voltage to 12 volts.
  • 200 Volt Thyristor.
  • Control buttons.

Connected to the mains using a diode bridge and transformer. Thyristor circuit and contact diode group in the inverter raises the voltage, after which the current is fed through the cable to the working welding gun.

Transistor diode unit used must be able to withstand the highest current output, which reaches 1500 Amperes. Control the output power of the welding current can be achieved with a bus, which is installed instead of the secondary winding.

Despite the apparent complexity, even the initial skills of reading wiring diagrams and work with radio components will be enough for self-made spotters, which can be used not only in everyday life, but also to perform various kinds of bodywork.

It is only necessary to choose a high-quality circuit of the contact welding machine, and then fully adhere to the available documentation.

Enclosure and cables

The box of a self-made spotter can be made of available metal materials. The easiest way to do this is to use a case from an old computer. The presence of a working fan will be an additional plus, which will reduce the temperature, allowing you to improve the duration of operation of the device without shutting it down for mandatory cooling.

Inside the case it is necessary to install several fans, which work from 12 volt and allow for good cooling of the power part of the inverter. The easiest way is to use computer fans that are directly connected to the control unit and run continuously or on the signal from temperature sensors.

The presence of compact fans inside the enclosure allows for longer continuous operation of the unit at maximum power ratings.

Welding cables are best to use pre-purchased with a cross section of not less than 1 millimeter per 10 Ampere capacity of the maximum current indicators. For the mass use cables with a length of not more than 150 centimeters, and the working wire is not longer than 250 centimeters. Otherwise, there can be a loss of amperage, which will adversely affect the performance of the machine and the quality of the weld.

Threaded connections are attached to both ends of the cable to secure the welding gun and connect it to the inverter. The quality of the connection must be given due attention, because the loss of welding current depends on it. On the reverse side of the power cable for the ground, install a quick-connect clamp or use threaded terminals.

Executing the work gun

The main working element of the spotter is the welding gun, which allows spot heating of the metal. If you plan to constantly use the equipment, it is preferable to buy a ready-made factory gun, which has a simple design, reliability and durability. If the spotter is made for occasional use, it is quite possible to assemble a working gun from improvised devices.

The easiest way to make it from a glue gun, which attached a strong and comfortable handle of textolite or other non-conductive materials. The appropriate holes are made in the glue gun for the guides, to which the electrode to be used is subsequently fastened. The cable from the inverter is connected to the gun and, when the trigger is pulled, a short powerful pulse is emitted.

The holding bracket that fastens the welding electrode is made of a rectangular or square copper tube. Copper bars with a diameter of 8-10 millimeters are used as electrodes.

You can find different schemes and options for making a contact welding gun, which involve changing the electrode without disassembling the made device.

Assembly of the reverse hammer

One of the advantages of using a spotter is the quick exchange of tools, which extends the functionality of such equipment. To perform leveling and welding bodywork a reverse hammer, or as it is also called inopuller, is used. It is easy to make a simple reverse hammer with your own hands. It is made on the basis of a metal mounting gun.

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From the old mounting gun cut off the part that holds the cylinder with sealant and assembly foam. Three bars, no more than 10 millimeters in diameter, are welded to the vacated pad. To the free ends of the rods fix a ring by welding, which is made from a rod with a cross section of 6-10 millimeters. The diameter of the ring should not exceed 100 millimeters.

At the rod of the gun cut stops and curved part. Instead of them welded mount, to which subsequently connect the cable from the welding inverter. Two nuts and a bolt with M10 thread can be used to fasten the cable.

A reverse hammer can be used to perform high quality spot welding and straightening work without damaging the original paintwork.

If you want, you can buy ready-made reverse hammers, which differ in diameter of the working body and are designed for use on spotters with different power.

How to make a spotter for auto body repair

There are several options for making a spotter for auto body repair out of used old units. Let’s look in detail at the different assemblies.

Which accessories do you need?

In order to provide the spotter with source of current, we will need a transformer for about 1500 A, as well as a working tool that will directly perform the straightening. If you don’t have such a transformer, you will have to rewind it yourself.

The scheme of the device spotter for body repair with his hands

In addition to the transformer and reverse hammer (we’ll show you how to make it below), you need a control unit (it contains a thyristor 200 V), a diode bridge, a contractor (220 V), as well as a 30 A relay.

Parameterizing and rewinding a transformer for a spotter with your own hands

The biggest difficulty in adapting the transformer for welding is to increase the output current to 1500 amps. For this purpose, experiment with a busbar to be installed in place of the secondary winding. Rewinding a transformer is the most labor-intensive step. Usually copper or aluminum wire is chosen for this purpose.

Winding a transformer for a spotter with copper wire

reverse, hammer, spotter, hands

For your information! A cross-sectional area of at least 160 mm² is considered ideal, and the voltage in the busbar should be 6 V.

To protect your spotter from sudden failure, and yourself. from electric shock, the primary and secondary windings of the transformer isolate from each other. Usually for this purpose they take a lacotta fabric or several layers of paper impregnated with paraffin. The magnetic circuit, which is the basis of such a transformer, must have an operating cross-section of at least 400 mm², and its dimensions are calculated taking into account the location of the windings.

“The productivity of the device also depends on the parameters of the wires. the shorter and thicker they are, the more effectively the unit will function.

For a W-shaped core, the primary winding of the transformer, consisting of 200 turns, is made of 2.5 mm² wire.

reverse, hammer, spotter, hands

Types of transformer magnetic cores and their dimensions for calculating the cross-sectional area

The secondary winding has 7 windings for which a 50 mm² wire or a busbar with corresponding cross-section with insulation is used. The length of the output ends of the transformer’s secondary winding should allow it to be connected to the output terminals, and the primary winding should allow it to be connected to the electrical circuit of the machine. It is desirable to impregnate the transformer you have made with shellac.

Fabrication of the control unit

The most important thing when assembling the control unit is to correctly connect the jumpers to break the primary contacts. The simplest and more complicated circuits may be used. We showed them above.

Fixing the jumpers on a 12 Amp circuit breaker

Usually the control box is wired to the start button and the quick-start switches, which are led to the housing. Coolers are installed, if necessary, and the ground wires are hidden.

Choosing the spotter enclosure and the power wire

The housings for the spotter can be used in a variety of ways. Some people take the case from a PC, it’s convenient because it already has the ability to install microchips and coolers, others make a box of metal plates or even wooden blocks. The size of the enclosure can be chosen arbitrarily, depending on the size and number of transformers and additional parts. A dielectric plate is used in the base of the housing, on which all the working elements are mounted. The main criterion for selection becomes not the aesthetics of the design, but the possibility of unimpeded access to all elements.

Options for homemade housings for spotters:

You often see cases from old microwaves, welding machines, batteries, system units. When selecting a welding cable, the following calculation is best: 10 Ampere of maximum allowable current from the spotter should be 1 mm² of cable cross-section. For the mass, you should use a cable that is no longer than 1.5 m, for the worker. no more than 2.5 m. If you neglect these requirements and use a longer cable, this will lead to a significant loss of welding current.

How to Make an Electrode

It, too, can be made with your own hands. Usually round copper bars, bronze or copper tubes are used, which are very convenient to connect to the current-conducting cable. At the side of the electrode’s working part, a slot must be made into which the welding washer will be inserted. If you use a tube to make an electrode, then its working end must be flattened, and only then make on it the appropriate slot.

Attachment of components depends on whether it will be a stationary device or portable. If you choose the second option, the components are distributed evenly and assembled with the help of fasteners. Handles for transportation are installed on the outside of the housing.

Making a working welding gun

The welding gun is the main working device of the spotter. If you plan to use the device actively enough, it is better to buy a ready sample. But for works of small volume, a homemade device is quite suitable. A glue gun or the working part of a semi-automatic welder is used as the base. Here is the easiest way to assemble a handle for your spotter with your own hands.

Illustration: Description of action
Take metal pipe of the necessary diameter and length as a basis.
Find unnecessary shape, which can become a tracing paper for the future gun, and outline on the board.
Cut out the workpieces with the jigsaw and file away any burrs if necessary.
Duplicate our workpieces on the metal.
Wrap up by welding and check for alignment.
Drill the holes.
This is what our gun for the spotter looks like assembled.

The gun should have such a design, which would allow you to change the electrode without disassembly. By the way, it is better to make the electrode of copper, usually its diameter is 8-10 mm. To connect the gun to the device, use a combination of a welding cable with the required cross section and a 5-core control cable. Connect the latter according to the diagram. If you plan a large amount of work, then you will need the schemes and drawings of the puller for the spotter, with your own hands they are very easy to make.

Usually for the base you take a ready-made machine, a cone-shaped nozzle is welded on it. These samples can be bought ready-made, or you can weld them yourself

Making a reverse hammer for the spotter with your own hands

In this case we put a heavy bar on the electrode. It will be a reverse hammer. Most often metal rods are used to make it. At the end of the electrode you need to weld a sharp tip, which makes contact with the surface of the body when straightening cars. Here is a short instruction on how to make a reverse hammer.

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Illustration How to do it
We take two bars: 16 and 12 mm in diameter. For the work we will need nuts with 12 threads. And also some large washers.
We weld the metal bars together to make a cylinder that moves freely around the base. A stop is welded on the bottom side.
The nozzles can be changed with the help of screwing screws. Arrowheads with a sharp end are used for bodywork.

The key part of the spotter

The welding gun is the main part of the device. For continuous operation, a factory-made device is used. It is possible to make it on the basis of a construction glue gun with your own hands. An alternative method would be to use parts from semi-automatic welding. Identical parts with lengths from 12 to 14 mm are cut out of textolite. There should be two of them. They are fitted with a bracket used as an electrode mount for welding. If desired, a bulb for illumination can be assembled, as well as a pulse switch.

Bracket can be made of copper. It can have a rectangular or square cross-section. Copper rod with a thickness of 8 to 10 mm is used as a welding electrode. The gun must be designed in such a way that the electrode can be changed without disassembly. To connect the gun to the device, use a combination of a welding cable with the required cross section and a 5-core control cable. Connect the latter in accordance with the diagram.

Three wires are routed to the switch. Two more wires go to the illuminating bulb and the motor. The welding cable must be stripped and soldered into a special hole in the bracket.

Case of the self-made spotter and other accessories

Even if you make the spotter yourself, you need to take care of the housing. First of all, you need to make a base for your equipment, for which you can use a board of dielectric material. It is important to size the base so that it can accommodate all the components of the spotter, and have easy access to the places where installation will be carried out. To do this, you can pre-prepare a drawing, drawing in scale all the structural elements of the device.

To protect all the internal components of your self-made spotter and make it aesthetically pleasing, it is convenient to use the housing from an old microwave oven or welding machine. If you plan to carry your spotter often, you need to distribute the weight of its internal components evenly and provide secure fastenings for a strap or carrying handle. In addition, you can mount small wheels on the bottom of the base of the device, which will also make the machine more mobile.

Home-made spotter enclosure option

Once you have made your spotter with your own hands, you need to equip it with additional accessories, which include:

When selecting welding cables, it is very important to choose the right cross section. For this purpose, a simple calculation can be made: for 10 A of maximum allowable current, which the spotter produces, there must be 1 mm 2 cable cross-section. For the weight you should use a cable that is no longer than 1.5 m, for the worker. no more than 2.5 m. If you neglect these requirements and use cables of greater length, it will lead to a significant loss of strength of the welding current, which will negatively affect the quality of performance of welding work.

Connecting elements must be securely fastened to the cable ends. These can be screw terminals or devices which provide a quick connection to the corresponding terminals on the machine and its operating element, the gun. On the back of the cable for the mass, you can install a quick-release element (crocodile) or equip it with a terminal for threaded fastening.

Algorithm of manufacturing with their own hands

To build a machine yourself, you need some skills and understanding of the basics of working with such equipment. The spotter from a welding machine with your own hands can be made according to the drawings. To do this, you must carefully study the design features of the apparatus. You can use improvised parts.

It is not always advisable to purchase a factory-made device. A quality unit can cost a pretty penny. It is necessary to consider the configuration of the device and its drawings.

Equipment made from an inverter unit

Most often, an inverter-based unit is made using homemade material. The main components of the device are a thyristor relay and a welding inverter. To assemble the device you will need:

  • a thyristor with a value of 200 volts;
  • Transformer to lower 122 volts to control the relay by means of a pushbutton;
  • Relay with a capacity of 30 amps;
  • bridge on diodes;
  • A pushbutton for control and monitoring;
  • 220 volt contact group.

A transformer must be connected using a diode bridge. A thyristor relay is connected to it. The transformer feeds the control circuit branch. Before making the spotter with your own hands, you must ensure safe working conditions. To this end, put rubber mats under the feet and adhere to standard safety rules.

Basic assembly steps

To make a homemade unit, a Nordic welding machine is ideal. It is necessary to be able to change the configuration of the device so that the DC spotter at the output gives 1500 amperes, at least. The assembly is carried out according to the following rules:

  • Remove the secondary layer from the machine. Sometimes there is more than one.
  • Before installation, determine the number of turns per 1 volt. The primary winding for this is wrapped with copper wire. Then measure the Volts.
  • Divide the figure obtained by the number of turns. The result is the number of turns per Volt.
  • From the secondary layer, which has been removed, produce a tire. It is desirable not to allow this parameter to fall below 160 square millimeters.
  • The voltage must be 6 volts. If the cross section is smaller, you can divide the bar into several parts. They are fastened together with insulating tape.

The number of fragments depends on the initial indicators. Let’s assume that if the parameter is equal to 40 kV. mm., The busbar is cut into 4 parts. It is necessary to take two tires with a wrap of duct tape or masking tape for painting works. Insulation should be consistent. First comes a layer of insulating tape, then duct tape, and then tape on top. Rivets can be installed on the exposed areas.

The busbars obtained are moved onto the transformer. This process is not easy and requires certain skills. A hammer and an extra helper are needed. This ensures that the busbar will fit better and will not be damaged in any way. If the power indicator is normal, the fixture can be considered ready. If not, you will have to conduct a number of experiments, connecting to the primary winding wires.

Home-made spotter made from battery and retractor relay

If your activity, one way or another, is related to the correction of the geometry of parts on the car body, the best assistant in this matter will be a spotter. This spot-welding machine will help you return body parts such as:

The main advantage of using the spotter for auto body repair, is the ability of the device to level the surface, having access only to its outer part. It allows you to repair any structural part. Such a device is equipped with a reverse hammer.

The principle of operation of the device is the following: it is welded to the metal surface of the car and with the help of pointwise impact centimeter by centimeter pulls the metal.

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Body sheeting home-made spotter from the battery All work is fast and does not require zazvelivaniya technological holes, which are designed for the straightening of metal. In addition, you do not need to attach additional accessories to the body of the car.

If you are in the auto repair business, you probably have a lot of customers. To speed up the work on the alignment of dents, you need:

Make a spotter with your own hands is quite realistic, using the right scheme.

And homemade spotter will not be inferior to purchased, but it will cost you several times cheaper. All you need is an old battery of high power.

Battery for the homemade spotter

Needed material

From familiar auto service workers, you can often hear that the battery-powered spotter is in no way inferior to the usual. Take for it is desirable to an old battery: first, it is not sorry, and secondly, it will operate at a current close to the short circuit current. Of course, the service life of such a product will be shorter than the operation of an ordinary spotter, but the money spent on the purchase will be more than offset by the reduced costs of repairing the car.

To make a battery spotter, you will need:

  • battery. A 75Ah or higher model will do;
  • retracting relay. Use the accessory from the auto starter;
  • battery charger;
  • A wire made of copper with a cross-section greater than 100 m2;
  • reverse hammer. It can be replaced by a gun, welding washers.

Electrical scheme of the spotterThe spotter from the battery and the retracting relay is connected as shown in the diagram, namely:

  • The relay body is connected to the minus terminal, as well as a wire no longer than 1.5 m. At the end of the wire contains a contact intended for the body of the part that will be pulled. It is a good idea to use copper thread contact to ensure that there is minimal resistance at the point of contact with the part;
  • The plus terminal is connected to the relay with your own hands using a bolt. The second bolt from the relay attaches the wire going to the return hammer or gun. The plus cable must not be longer than 2.5 meters. This will reduce the voltage drop in the cable;
  • Run a wire from the positive terminal to the control contact as well. Finish the wire with a button, which will control the battery spotter. The length of the conductor for the button is not strictly fixed.

The retractor relay is mounted on the battery to connect multiple contacts. If you have the option, install a collapsible relay that you can remove and clean at any time. If it is possible to pull out its inner part, it needs to be shortened and crimped. This prevents the rod from being lost. This is the end of all relay transformations.

You also need to hand mount the button to control the pulse.

This is either mounted on the wire itself or on the gun. Connection of the part is made from a positively charged wire (in a car, the cable from the ignition switch comes to this contact). There are no specific requirements to the properties of a homemade button. you need it to be able to withstand 5-7A of current.

Drawing relay for the battery spotter

Also consider the wires. Work with them will be effective if you take a short and thick cable. Its length should be less than 1.5 m and be limited to losses in the product itself, because welding is characterized by high currents.

The welding gun can be made with your own hands even from wood, and a washer fixture can be made from brass or copper. You can use a tube from an air conditioner, and make a slit at the end of the small tube. This will allow you to conveniently insert the washer in place.

Before you start, charge the battery. Accordingly, after work, put the device to charge again.

Consumable kit for the spotter

Advantages and disadvantages

Made by our own hands the spotter has these advantages compared to the purchased counterpart:

  • low level of costs in the production of the device;
  • the possibility of making the device at home, even if you have no experience with electronics;
  • The possibility of working in the place where there are interruptions in the electricity (garage).


However, the disadvantages of homemade equipment are also sufficient. Among them, experts highlight:

  • The absence of a temporary relay;
  • the permanent need to charge the battery;
  • A shorter period of operation of the device;
  • switchable contact of the operating current;
  • The inability to adjust many parameters, among which the current strength.

To reduce the cost of making a homemade device, some people make a spotter from a transformer that stands in a microwave oven. Many are skeptical of such equipment, as they believe that it will not be able to provide the necessary amount of working current. This is due to the smaller size of the transformer iron section.If you are not suited to the battery option, you can try to make a technique from a light transformer or from a welding machine, by rewinding the secondary winding. The current intensity in such a device must reach at least 500A. [inverter]

Education: high school. Specialty: auto locksmith. Professional diagnostics, repair, maintenance of foreign-made cars 2000-2015.в. Great experience with Japanese and German cars.

What is a spotter and how to use it

Spotters visually represent a machine that consists of a box, cable, gun (staddy) and a sharp rod (electrode). In the box is the entire system of the welding machine, including transformers or inverter. The process of spot welding for auto bodywork itself looks like this: a fixture is welded on the damaged metal, the spotter is attached to it, and the dent is pulled out with additional mechanisms or manually. This method is convenient when it is inconvenient or impossible to level the surface of the body from the inside. There are many advantages to working with such specialized equipment. minimum effort, fast and without risk of more damage.

In order to make the bodywork of the car as quickly and accurately as possible, it is necessary to follow a certain order and technology of the process, as well as take into account small nuances:

  • The surface that has been deformed must first be cleaned of any kind of coating (varnish, paint, rust). This stage of the work is very important, because the quality of the connection between the two metals will also depend on the result of the whole process.
  • A ground contact should be attached to the surface that is to be corrected.
  • On the already cleaned surface of the damaged area of the metal should be welded a fixture, through which the spotter will be attached.
  • To the welded fastener, a grip is made with the spotter’s gun, after which the dent is pulled out. To correct the surface use a reverse hammer, hydraulic cylinders, staples and so on. Given the thickness of the metal, you need to determine what is the best tool to straighten the dent, so as not to damage the body. Let’s say a reverse hammer can’t be used for aluminum, and not every spotter will take a galvanized body.
  • After the body alignment is complete, the welded part is twisted and the contact area is ground with a grinder.

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